Galfan - Enhanced formability and corrosion resistance

Galfan (ZA) is a zinc-aluminium alloy coating that provides excellent corrosion protection and forming properties compared to traditional zinc coating.

Galfan coating features excellent corrosion resistance compared with traditional zinc coating. This is why it can be used to achieve a longer service life for a steel part, or to replace traditional zinc coating with a thinner Galfan coating, thereby simultaneously offering improved weldability and formability properties.

Galfan coating can be recognized by its bright metallic and mildly cellular-patterned surface. The eutectic composition of 95% Zn and 5% Al improves the coating adhesion and enables a lamellar coating structure in micro-scale, which makes it a ductile and well-suited coating for deep drawing. Galfan provides clearly enhanced formability compared with the traditional zinc coating.

Galfan coating is produced both-sided in a continuous hot-dip coating process. Because of the sacrificial nature of the Galfan coating, it provides corrosion protection for areas of exposed steel surfaces, such as cutting edges and possible areas where coating has damaged (scratches, impacts, etc.). Full corrosion protection is also achieved in areas that have been heavily formed because the peeling tendency of low-friction and tightly bonded coating is low.

SSAB offers Galfan coatings with different coating thicknesses, surface qualities and surface treatments to meet the demands of various applications.

Coating thickness

Coating designation Minimum total coating mass,
both surfaces (g/m2) *
Guidance value for coating thickness per surface,
typically (μm)
ZA095 95 7
ZA130 130 10
ZA155 155 11
ZA185 185 14
ZA200 200 15
ZA255 255 20
ZA300 300 23
* in triple spot test

In addition to these Galfan coating thicknesses defined according to EN10346:2015, the offering contains different asymmetric coatings, coatings with equal coating minimum mass per surface, and other OEM specifications that are available upon request.

Processing of Galfan coated steel

Forming

Usually the same forming processes as for un-coated steels can be applied for zinc-based coated steels without any substantial modifications to the process conditions. Little differences in surface behavior may require some changes for instance in lubrication, tooling geometry and holding forces. The metal coating has an advantageous characteristic of serving as lubricant, which works greatly with low and moderate surface pressures taking place in forming.

The lamellar microstructure of the Galfan coating is extremely well suited to roll forming, demanding deep drawing, profiling and bending. Due to the thin intermetallic layer at the interface of the steel and the coating, Galfan coating features great cracking resistance. These two properties makes Galfan the coating of choice for demanding forming operations.

The successful forming of metal coated steels is depending on selections made regarding the geometry of the component, steel grade, metal coating type and thickness, surface quality and protection, and a tool used in the forming.

Welding

Generally metal coated products can be welded by various welding techniques including different resistance welding, laser welding and arc welding. When welding recommendations are followed, the mechanical properties of welded joints are equal to those of non-coated steel. Galfan (ZA) coated steels can be welded using the same parameters as for zinc (Z) coated steels. If the coating thickness is reduced by using Galfan, the required welding current is lower and the service life of welding electrodes can be lengthened.

Resistance welding methods, like spot welding, are most common and giving excellent results with metal coated steels. Advantageous anticorrosion properties of the zinc-based coating mainly remain in the area of the properly made spot weld. Spot welding of metal coated material requires slightly higher current and electrode force than for uncoated steels due to the lower contact resistance of the coating. Similarly the increase in coating thickness increases slightly the required welding current. Therefore, in order improve weldability and achieve longer service life of welding electrodes, it is recommended to avoid unnecessarily thick coatings in welding applications.

Laser welding is also ideal for metal coated materials thanks to the narrow (only few mm) weld and low heat input. When any fusion welding methods are used, the heat input shall be as minimal as possible in order to limit the heated zone in the metal coated sheet. Similar to scratched areas of the coating, also in the narrow weld the sacrificial effect of the zinc-based coating provides cathodic corrosion protection. However, the weld area is recommended be painted or protected by other appropriate coating after the fusion welding process.

Ventilation of the workplace must be arranged properly because welding of zinc-based coated steels produces welding fumes containing zinc oxide.

Joining

All zinc-based coatings are well suited for adhesive bonding provided that the surface is matched with the adhesive (epoxy, acrylic or polyurethane adhesive) used. One advantage of adhesive bonding is that it preserves the anticorrosion properties of the coating because the coating basically remains intact in the joint area. In order to ensure good adhesion, any oils or impurities should be carefully removed from the surfaces to be adhesively bonded. Thin organic coating (TOC) is recommended in many cases providing best surface for adhesive bonding. The compatibility of the surface with the adhesive used shall always be considered case by case.

Regarding mechanical joining, both tab (e.g. bolt or rivet) and non-tab methods are equally applicable for Galfan. For example, lock-seaming, folding, tab and compression joints are all suitable for Galfan, due to its superior formability. Regarding soldered joints, flame or arc soldering can be used for Galfan. Adhesives used for zinc coated steel are also applicable for the Galfan coated steel.

Painting

In addition of providing the desired color for the final product painting further improves the corrosion protection of the final product. Similar to zinc (Z) coating, Galfan (ZA) provides a good substrate for painting when appropriate paints are used. The same paints and painting methods are applicable as with the zinc (Z) coated steels. The skin passed surface quality B is recommended when high surface quality for the painted surface is required.

In order to ensure good adhesion, any oils or impurities should be carefully removed from the surfaces to be painted. The product can be pre-treated by zinc-phosphating or alternative pretreatment suitable for zinc-based coated steels in receiving plant to facilitate the coating adhesion.